The present invention relates to a formed copper catalyst for the selective hydrogenation of furfural to furfuryl alcohol and more particularly to a shaped catalyst containing an intimate mixture of reduced copper and a high-surface carrier material.
Furfuryl alcohol is an important selective solvent and is used as an initial starting material for the production of adhesives, paints and coatings. It is obtained by the catalytic hydrogenation of furfural.
The hydrogenation is carried out on an industrial scale either in the gaseous phase or in the liquid phase on a fixed-bed reactor. The conversion, yield and selectivity of this reaction are quite dependent on the process conditions selected and on the purity of the furfural. Superelevated reaction temperatures can result in undesired side products such as e.g. 2-methyl furane, tetrahydrofurfuryl alcohol and ethers by ring cleavage. Low-grade furfural used as the starting material can contain rather high amounts of acetic acid and sulfur, which result in a premature poisoning of the catalyst.
Suitable catalysts for the hydrogenation of furfural are copper chromite catalysts, Raney Ni, Raney Co and Raney Cu catalysts as well as copper catalysts promoted with sodium silicates.
U.S. Pat. No. 2,754,304 describes a catalyst for the gaseous-phase hydrogenation of furfural to furfuryl alcohol. The catalyst consists essentially of reduced copper promoted with a rather low amount of sodium silicate. It is produced by mixing copper(II) oxide with 5 to 20% by weight sodium silicate, forming this mixture into tablets and by subsequently reducing the copper(II) oxide to metallic copper. Heated hydrogen gas is passed over the catalyst tablets for the reduction. Conversions of over 99% are obtained with this catalyst in the gaseous-phase hydrogenation of furfural.
U.S. Pat. No. 4,185,022 describes a further development of this catalyst. It consists of a neutral or alkaline, inorganic carrier material with a specific surface of at least 60 m.sup.2 /g prior to the deposition of a copper/sodium silicate component onto this carrier. The copper/sodium silicate component consists of 5-20% by weight sodium silicate. The finished catalyst contains at least 8 but not more than 25% reduced copper. Pumice, silica gel, quartz and neutral aluminum oxide are cited as suitable carrier materials. Pumice is the preferred carrier.
German Offenlegungsschrift DE 41 42 897 A1 corresponding to U.S. Pat. No. 5,407,886 describes porous catalytic formed bodies containing a metal of the iron group and/or copper on a carrier consisting of oxide or silicate, especially of pyrogenic silica.
The metal content of the formed bodies is 5 to 40% by weight relative to their total weight. The metal crystallites on the carrier exhibit a size of .ltoreq.3 nm. This small size of the metal crystallites is assured by a special production process wherein precursor compounds of the metals are deposited by a hydrolysis precipitation in a suspension of the powdery carrier material on the carrier material. After shaping of the powdery carrier material into formed bodies the latter are calcined at temperatures between 300.degree. and 500.degree. C. and reduced in a current of hydrogen at temperatures between 400.degree. and 450.degree. C. The catalysts obtained in this manner are suitable for the hydrogenation of hydrocarbons.
An object of the present invention is to make available a chromium-free catalyst for the hydrogenation of organic compounds, especially for the selective hydrogenation of furfural to furfuryl alcohol.
Another object of the invention is to make a catalyst with improved specific catalytic activity over the known chromium-free catalysts and which can hydrogenate furfural to furfuryl alcohol with elevated selectivity and an improved yield.